With internal combustion engines, a catalytic aftertreatment of the exhaust gases has become established to comply with the legally prescribed emission values. Modern internal combustion engines often operate with lean fuel-air mixtures, e.g., with an excess of oxygen, in order to increase efficiency. Oxides of nitrogen that occur cannot be reduced in the lean mode with CO or HC, because the catalytic reduction thereof in the NOx storage catalytic converter is only possible in a rich mode. Therefore, in the lean mode the oxides of nitrogen in the exhaust gas are temporarily stored in a NOx storage catalytic converter, also referred to as a lean NOx trap (LNT). If the absorption capacity of the LNT is exhausted, a cycle is carried out for the regeneration of the LNT with a rich exhaust gas mixture or in a substoichiometric mode (λ<1). Such a regeneration is also referred to as a rich purge. In this cycle, the temporarily stored oxides of nitrogen are reduced to nitrogen and the catalytic converter is again ready for the storage of oxides of nitrogen.
It is often problematic, however, to maintain the rich purge for long enough so that the regeneration of a LNT can be fully carried out. Gas exchange and gear changing by a driver make the control of the regeneration difficult. This particularly applies to a dynamic manner of driving with frequent operation of the accelerator pedal. It is usual to start a regeneration of a LNT at a low acceleration, whereby a uniform increase of the target torque is possible for a small amount of additional re-injection of fuel. On the other hand, an aggressive manner of driving is unfavorable, because the torque cannot be maintained for long enough before the next gear is engaged. Even at low acceleration, however, an interruption of the regeneration can occur, for example if a change is made into a braking phase. This means that a new regeneration has to be started in order to reduce the oxides of nitrogen completely, which has an adverse effect on the fuel consumption.
The inventors herein have recognized the above issues and provide a method to at least partly address the issues. In one example, a method includes, responsive to a first condition: detecting a first speed of the motor vehicle; activating the adaptive cruise control system and setting the adaptive cruise control system to a second speed and detecting a distance to a preceding vehicle; increasing the distance to the preceding vehicle if the distance is less than a target distance; starting an acceleration phase while simultaneously starting regeneration of the NOx storage catalytic converter if the distance to the preceding vehicle is greater than the target distance and the first speed of the vehicle is less than the second speed; and maintaining the acceleration phase until a target speed is reached, a gradient of the acceleration of the motor vehicle controlled such that the regeneration of the NOx storage catalytic converter is completed in the acceleration phase.
In this way, adaptive cruise control is used advantageously in order to control the distance to a preceding vehicle ahead of the motor vehicle in which the LNT regeneration is carried out. During operation with adaptive cruise control, the speed of the motor vehicle is reduced, if a vehicle ahead has been identified, in order to achieve or maintain a predetermined distance, e.g., a target value of the distance. If the target value of the distance is reached or exceeded, the motor vehicle is accelerated until the target value of the speed is reached. LNT regeneration may then be carried out during this controlled acceleration. Owing to the method, the regeneration of a NOx storage catalytic converter can be controlled advantageously without being interrupted by an irregular manner of driving or aggressive acceleration. Owing to the full regeneration of the NOx storage catalytic converter, it is again ready to receive oxides of nitrogen from the exhaust gas. At the same time, the fuel consumption is reduced by the uninterrupted regeneration.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.